RIⅤ ALROUS NONRIVALROUS NWI NEl Uncongested Private Good Uncongested Toll Good Nw2 NE2 9 Efficient Market Supply No private supply at Congested Congested: efficient price of zero; underconsumption Private Good with at any positive Toll Good with DrIce Crowding Consumption externality Private supply can be Overconsumption because efficient if price at marginal consumers respond to price social cost; peak-load pricing rather than marginal social cost required if congestion variable Uncongested"Free Good SWI SEl Supply exceeds demand sw2 Uncongested: Pure Public GoodD SE2 Private supply unlikely s at zero price; no Congested: because exclusion not e inefficiency until Dpen Access possible; some demand grows to Congested 义| exceed supply and Common private supply in at zero price. Property Resources privileged and,,'Ambient Public Good Consumers respond to intermediate with Consumption marginal private cost rather groups. Externality than marginal social cost overconsumption, rent dissipation Overconsumption because and underinvestment in presentation consumers ignore external cost Figure 5.2 A Classification of Goods: Private and Public